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The 3ω method is a well-established thermal technique used to measure the thermal conductivity of materials and the thermal resistance of interfaces. It has significant advantages over other steady state and transient thermal techniques in its ability to provide spatially resolved thermal property measurements over a wide range of thermal conductivity. Despite its advantages, it has been restricted to lab-scale use because of the difficulty involved in sample preparation and sensor fabrication and is limited to non-metallic substrates. High-throughput 3ω measurements with reusable sensors have not been realized yet. In this work, we demonstrate a method of applying reusable 3ω sensors fabricated on flexible polyimide films to measure bulk and spatially resolved thermal properties. We establish the limits of thermal conductivity measurement with the method to be 1 to 200 W/mK, and within the measurement limit, we verify the method by comparing the measured thermal conductivities of standard samples with established values. From the 3ω measurements, we also determine the thermal resistance of an interlayer of thermal grease as a function of pressure and compare it against the resistance calculated from direct thickness measurements to demonstrate the ability of this method to provide spatially resolved subsurface information. The technique presented is general and applicable to both metallic and non-metallic substrates, providing a method for high-throughput 3ω measurements with reusable sensors and without considerable sample preparation. [ABSTRACT FROM AUTHOR]

An improved method to simultaneously determine the heat capacity, thermal diffusivity, and thermal conductivity of a small-sized material is described. In this method, the heat of a square wave with a superimposed constant component is applied to one side of a plate-shaped sample using a thin-film heater, which is thermally linked to a heat reservoir. The response temperature is measured by a thermometer attached to the heater. In contrast to a previously reported method, the amplitude of the temperature oscillation detected by the thermometer is enhanced by the internal thermal relaxation in the improved method. This feature is advantageous for determining thermal properties with low-heat modulation. We theoretically analyzed the proposed method using a one-dimensional model and demonstrated the method on synthetic quartz (SiO2) and poly(methyl methacrylate) plates in the temperature range of 80–300 K. The thermal properties obtained for both samples using the proposed method were consistent with values reported in the literature. The deviations from the data for the specific heat capacity, thermal diffusivity, and thermal conductivity were estimated to be ∼1%, 2%, and 2%, respectively. [ABSTRACT FROM AUTHOR]

High heat fluxes generated in electronics and semiconductor packages require materials with high thermal conductivity to effectively diffuse the heat and avoid local hotspots. Engineered heat spreading materials typically exhibit anisotropic conduction behavior due to their composite construction. The design of thermal management solutions is often limited by the lack of fast and accurate characterization techniques for such anisotropic materials. A popular technique for measuring the thermal diffusivity of bulk materials is the Ångstrom method, where a thin strip or rod of material is heated periodically at one end, and the corresponding transient temperature profile is used to infer the thermal diffusivity. However, this method is generally limited to the characterization of one-dimensional samples and requires multiple measurements with multiple samples to characterize anisotropic materials. Here, we present a new measurement technique for characterizing the isotropic and anisotropic in-plane thermal properties of thin films and sheets as an extension of the one-dimensional Ångstrom method and other lock-in thermography techniques. The measurement leverages non-contact infrared temperature mapping to measure the thermal response from laser-based periodic heating at the center of a suspended thin film sample. Uniquely, our novel data extraction method does not require precise knowledge of the boundary conditions. To validate the accuracy of this technique, numerical models are developed to generate transient temperature profiles for hypothetical anisotropic materials with known properties. The resultant temperature profiles are processed through our fitting algorithm to extract the in-plane thermal conductivities without knowledge of the input properties of the model. Across a wide range of in-plane thermal conductivities, these results agree well with the input values. Experiments demonstrate the approach for a known isotropic reference material and an anisotropic heat spreading material. The limits of accuracy of this technique are identified based on the experimental and sample parameters. Further standardization of this measurement technique will enable the development and characterization of engineered heat spreading materials with desired anisotropic properties for various applications. [ABSTRACT FROM AUTHOR]

The thermal conductivity and thermal diffusivity of both metallic and non-metallic microwires are simultaneously measured by a cross-wire geometry. In this method, the heating wire serves both as a thermometer and a heater. The deflection of the heating wire is in situ modified by using the Ampère force to contact and separate the test wire. By using the quasi-steady-state measurement, the thermal contact resistances under different contact conditions are obtained so that the effect on thermal conductivity can be eliminated. This method is verified by both the metallic wires and carbon fiber to clarify the effect of the surface radiation heat loss of the test wire. The obtained thermal properties are repeatable though the magnitude of the thermal contact resistance under different contact conditions changes significantly. The cross-wire geometry overcomes the obstacle introduced by different thermal interfacial materials, which provides an accurate and convenient way to measure the thermal properties of microwires. [ABSTRACT FROM AUTHOR]

In a frequency-domain thermoreflectance (FDTR) experiment, the phase lag between the surface temperature response and the applied heat flux is fit with an analytical solution to the heat diffusion equation to extract an unknown thermal property (e.g., thermal conductivity) of a test sample. A method is proposed to reduce the impact of uncertainty in the laser spot radius on the resulting uncertainty in the fitted property that is based on fitting to the quotient of the test sample phase and that of a reference sample. The reduction is proven analytically for a semi-infinite solid and was confirmed using numerical and real experiments on realistic samples. When the spot radius and its uncertainty are well known, the reference phase can be generated numerically. In this situation, FDTR experiments performed on Au–SiO2–Si and PbS nanocrystal test samples demonstrate 32% and 82% reductions in the overall uncertainty in thermal conductivity. When the spot radius used in the test sample measurement is not well known, a real reference sample, measured under conditions that lead to the same unknown spot radius, is required. Although the real reference sample introduces its own uncertainties, the total uncertainty in the fitted thermal conductivity can still be reduced. A reference sample can also be used to reduce uncertainty due to other sources, such as the transducer properties. Because frequency-domain solutions to the heat diffusion equation are the basis for time-domain thermoreflectance (TDTR) analysis, the approach can be extended to TDTR experiments. [ABSTRACT FROM AUTHOR]

Measuring the thermal conductivity of sub-surface buried substrates is of significant practical interests. However, this remains challenging with traditional pump–probe spectroscopies due to their limited thermal penetration depths. Here, we experimentally and numerically investigate the TPD of the recently developed optical pump–probe technique steady-state thermoreflectance (SSTR) and explore its capability for measuring the thermal properties of buried substrates. The conventional definition of the TPD (i.e., the depth at which temperature drops to 1/e value of the maximum surface temperature) does not truly represent the upper limit of how far beneath the surface SSTR can probe. For estimating the uncertainty of SSTR measurements of a buried substrate a priori, sensitivity calculations provide the best means. Thus, detailed sensitivity calculations are provided to guide future measurements. Due to the steady-state nature of SSTR, it can measure the thermal conductivity of buried substrates that are traditionally challenging by transient pump–probe techniques, exemplified by measuring three control samples. We also discuss the required criteria for SSTR to isolate the thermal properties of a buried film. Our study establishes SSTR as a suitable technique for thermal characterizations of sub-surface buried substrates in typical device geometries. [ABSTRACT FROM AUTHOR]

The development of high thermal conductivity thin film materials for the thermal management of electronics requires accurate and precise methods for characterizing heat spreading capability, namely, in-plane thermal conductivity. However, due to the complex nature of thin film thermal property measurements, resolving the in-plane thermal conductivity of high thermal conductivity anisotropic thin films with high accuracy is particularly challenging. Capable transient techniques exist; however, they usually measure thermal diffusivity and require heat capacity and density to deduce thermal conductivity. Here, we present an explicit uncertainty analysis framework for accurately resolving in-plane thermal conductivity via two independent steady-state thermometry techniques: particle-assisted Raman thermometry and electrical resistance thermometry. Additionally, we establish error-based criteria to determine the limiting experimental conditions that permit the simplifying assumption of one-dimensional thermal conduction to further reduce thermal analysis. We demonstrate the accuracy and precision (<5% uncertainty) of both steady-state techniques through in-plane thermal conductivity measurements of anisotropic nanocrystalline diamond thin films. [ABSTRACT FROM AUTHOR]

A new approach to measure the cross-plane thermal diffusivity of a microscale slab sample, which can be fabricated by the focused ion beam and attached to a substrate, is proposed. An intensity-modulated pump laser is applied to heat the front surface of the sample uniformly, and the thermoreflectance signal is observed at the rear surface to evaluate thermal wave transport in the material. The thermal diffusivity can be obtained by fitting the phase lags of the experimental data with a theoretical model. The model was developed for the sample with thin-film coatings and heat transfer to the substrate. Although the absorbed heat can cause a significant DC temperature increase in the microscale sample, a thin-film coating with high thermal conductivity can effectively reduce the DC temperature increase within low thermal conductivity samples. To validate the method, we conducted measurements of a fused silica sample of 2.16 µm thickness, coated with 95 nm Ti film on the front surface and 120 nm Au film on the rear surface. The measured thermal diffusivity is in good agreement with the literature value. The uncertainty analysis shows that the measurement uncertainty is within 6%. This proposed approach, designed for microscale samples, offers a unique option for thermal property measurements of special materials, such as irradiated nuclear fuel or other irradiated materials, to enable microscale property determination while minimizing sample radioactivity. [ABSTRACT FROM AUTHOR]

Due to the limited size of samples prepared at the lab scale, characterizing the thermal properties of new materials may be problematic, and this makes it all the more difficult to optimize them. This statement especially applies to the development of innovative thermal (super)insulators. In this work, we demonstrate that the hot disk method, which might be preferred for such kinds of studies because of the low sample size it can allow in practice, is unable to provide realistic values of thermal conductivity in the case of insulators. A new method was thus developed, called Calibrated Tiny Hot Plate (CTHP). The corresponding heat transfers were modeled, and the two unknowns of the model were obtained by calibration with insulating samples whose thermal conductivity was precisely measured with a reference (guarded hot plate) method. We show that the CTHP is able to estimate conductivities within the range 0.014–0.2 W m−1 K−1 based on samples having thicknesses ranging from 3 to 9 mm and diameters as low as 15 mm. The accuracy was generally much better than 10%, which is a remarkable result for characterizing so small insulating materials. [ABSTRACT FROM AUTHOR]

Materials lacking in-plane symmetry are ubiquitous in a wide range of applications such as electronics, thermoelectrics, and high-temperature superconductors, in all of which the thermal properties of the materials play a critical part. However, very few experimental techniques can be used to measure in-plane anisotropic thermal conductivity. A beam-offset method based on time-domain thermoreflectance (TDTR) was previously proposed to measure in-plane anisotropic thermal conductivity. However, a detailed analysis of the beam-offset method is still lacking. Our analysis shows that uncertainties can be large if the laser spot size or the modulation frequency is not properly chosen. Here we propose an alternative approach based on TDTR to measure in-plane anisotropic thermal conductivity using a highly elliptical pump (heating) beam. The highly elliptical pump beam induces a quasi-one-dimensional temperature profile on the sample surface that has a fast decay along the short axis of the pump beam. The detected TDTR signal is exclusively sensitive to the in-plane thermal conductivity along the short axis of the elliptical beam. By conducting TDTR measurements as a function of delay time with the rotation of the elliptical pump beam to different orientations, the in-plane thermal conductivity tensor of the sample can be determined. In this work, we first conduct detailed signal sensitivity analyses for both techniques and provide guidelines in determining the optimal experimental conditions. We then compare the two techniques under their optimal experimental conditions by measuring the in-plane thermal conductivity tensor of a ZnO [11-20] sample. The accuracy and limitations of both methods are discussed. [ABSTRACT FROM AUTHOR]

We have designed and developed a new experimental setup, based on the 3ω method, to measure thermal conductivity, heat capacity, and electrical resistivity of a variety of samples in a broad temperature range (2–550 K) and under magnetic fields up to 9 T. The validity of this method is tested by measuring various types of metallic (copper, platinum, and constantan) and insulating (SiO2) materials, which have a wide range of thermal conductivity values (1–400 W m−1 K−1). We have successfully employed this technique for measuring the thermal conductivity of two actinide single crystals: uranium dioxide and uranium nitride. This new experimental approach for studying nuclear materials will help us to advance reactor fuel development and understanding. We have also shown that this experimental setup can be adapted to the Physical Property Measurement System (Quantum Design) environment and/or other cryocooler systems. [ABSTRACT FROM AUTHOR]

A new steady-state apparatus is designed and constructed for the measurement of thermal conductivity (up to 25 W/mK) on a square specimen (300 mm side) with a heating temperature range from 30 °C to 900 °C. A vacuum container, of which the pressure can reach to 1 Pa, is also built for materials which can be easily oxidized. The structure of the facility is different from that of traditional steady-state devices, especially for the design of heating plate and heat sink. To verify the temperature uniformity of the heating plate, a simulation analysis is carried out in this paper. Besides, the heating system, the heat sink, the measuring system, and the vacuum system are presented in detail. In addition, the thermal conductivities of a heat insulation tile, 304L stainless steel, n-docosane, and erythritol are measured by this apparatus. Finally, an uncertainty analysis is discussed depending on different temperatures and materials. [ABSTRACT FROM AUTHOR]

Commonly used thermal analysis tools such as calorimeter and thermal conductivity meter are separated instruments and limited by low throughput, where only one sample is examined each time. This work reports an infrared based optical calorimetry with its theoretical foundation, which is able to provide an integrated solution to characterize thermal properties of materials with high throughput. By taking time domain temperature information of spatially distributed samples, this method allows a single device (infrared camera) to determine the thermal properties of both phase change systems (melting temperature and latent heat of fusion) and non-phase change systems (thermal conductivity and heat capacity). This method further allows these thermal properties of multiple samples to be determined rapidly, remotely, and simultaneously. In this proof-of-concept experiment, the thermal properties of a panel of 16 samples including melting temperatures, latent heats of fusion, heat capacities, and thermal conductivities have been determined in 2 min with high accuracy. Given the high thermal, spatial, and temporal resolutions of the advanced infrared camera, this method has the potential to revolutionize the thermal characterization of materials by providing an integrated solution with high throughput, high sensitivity, and short analysis time. [ABSTRACT FROM AUTHOR]

Simplified heat-transfer models are widely employed by heated probe scanning thermal microscopy techniques for determining thermal conductivity of test samples. These parameters have generally been assumed to be independent of sample properties; however, there has been little investigation of this assumption in non-contact mode, and the impact calibration procedures have on sample thermal conductivity results has not been explored. However, there has been little investigation of the commonly used assumption that thermal exchange parameters are sample independent in non-contact mode, or of the impact calibration procedures have on sample thermal conductivity results. This article establishes conditions under which quantitative, localized, non-contact measurements using scanning thermal microscopy with heated microprobes may be most accurately performed. The work employs a three-dimensional finite element (3DFE) model validated using experimental results and no fitting parameters, to determine the dependence of a heated microprobe thermal resistance as a function of sample thermal conductivity at several values of probe-to-sample clearance. The two unknown thermal exchange parameters were determined by fitting the 3DFE simulated probe thermal resistance with the predictions of a simplified probe heat transfer model, for two samples with different thermal conductivities. This calibration procedure known in experiments as the intersection method was simulated for sample thermal conductivities in the range of 0.1-50 W m -1 K-1 and clearance values in the 260-1010 nm range. For a typical Wollaston wire microprobe geometry as simulated here, both the thermal exchange radius and thermal contact resistance were found to increase with the sample thermal conductivity in the low thermal conductivity range while they remained approximately constant for thermal conductivities >1 W m -1 K -1, with similar trends reported for all clearance values investigated. It is shown that versatile sets of calibration samples for the intersection method should employ either medium range (1 W m -1 K -1) and (2 W m -1 K -1) thermal conductivities, or wide range (0.5 W m -1 K-1) and (50 W m -1 K -1). The medium range yielded results within 1.5% –20.4% of the expected values of thermal conductivity for specimens with thermal conductivity within 0.1-10 W m -1 K-1, while the wide range yielded values within 0.5%-19.4% in the same range. [ABSTRACT FROM AUTHOR]

It is challenging to characterize thermal conductivity of materials with strong anisotropy. In this work, we extend the time-domain thermoreflectance (TDTR) method with a variable spot size approach to simultaneously measure the in-plane (Kr) and the through-plane (Kz) thermal conductivity of materials with strong anisotropy. We first determine Kz from the measurement using a larger spot size, when the heat flow is mainly one-dimensional along the through-plane direction, and the measured signals are only sensitive to Kz. We then extract the in-plane thermal conductivity Kr from a second measurement using the same modulation frequency but with a smaller spot size, when the heat flow becomes three-dimensional, and the signal is sensitive to both Kr and Kz. By choosing the same modulation frequency for the two sets of measurements, we can avoid potential artifacts introduced by the frequency-dependent Kz, which we have found to be non-negligible, especially for some two-dimensional layered materials like MoS2. After careful evaluation of the sensitivity of a series of hypothetical samples, we provided guidelines on choosing the most appropriate laser spot size and modulation frequency that yield the smallest uncertainty, and established a criterion for the range of thermal conductivity that can be measured reliably using our proposed variable spot size TDTR approach. We have demonstrated this variable spot size TDTR approach on samples with a wide range of in-plane thermal conductivity, including fused silica, rutile titania (TiO2 [001]), zinc oxide (ZnO [0001]), molybdenum disulfide (MoS2), hexagonal boron nitride (h-BN), and highly ordered pyrolytic graphite. [ABSTRACT FROM AUTHOR]

A novel heat-sinking, self-referencing fiber optic emission probe having a sapphire fiber probe head is described. The laser heating effect in a GaAs wafer (on a polytetrafluoroethylene (PTFE) platform) has been measured with the probe in both the noncontact proximity mode and the contact mode. The GaAs/PTFE composite was selected to simulate the thermal conductivity of animal tissues. It was found that for the same laser power delivered to the wafer, the temperature rise in the contact mode was only 42% of that in the proximity mode. Additionally, a demonstration of the self-referencing capability of the probe is also presented. [ABSTRACT FROM AUTHOR]

Accurate measurements of the cross-plane thermal conductivity Λcross of a high-thermal-conductivity thin film on a low-thermal-conductivity (Λs) substrate (e.g., Λcross/Λs > 20) are challenging, due to the low thermal resistance of the thin film compared with that of the substrate. In principle, Λcross could be measured by time-domain thermoreflectance (TDTR), using a high modulation frequency fh and a large laser spot size. However, with one TDTR measurement at fh, the uncertainty of the TDTR measurement is usually high due to low sensitivity of TDTR signals to Λcross and high sensitivity to the thickness hAl of Al transducer deposited on the sample for TDTR measurements. We observe that in most TDTR measurements, the sensitivity to hAl only depends weakly on the modulation frequency f . Thus, we performed an additional TDTR measurement at a low modulation frequency f0, such that the sensitivity to hAl is comparable but the sensitivity to Λcross is near zero. We then analyze the ratio of the TDTR signals at fh to that at f0, and thus significantly improve the accuracy of our Λcross measurements. As a demonstration of the dual-frequency approach, we measured the cross-plane thermal conductivity of a 400-nm-thick nickel-iron alloy film and a 3-μm-thick Cu film, both with an accuracy of ∼10%. The dual-frequency TDTR approach is useful for future studies of thin films. [ABSTRACT FROM AUTHOR]

Transient measurements of thermal conductivity are performed with hot disc sensors on samples having a thermal conductivity variation adjacent to the sample surface. A modified computational approach is introduced, which provides a method of connecting the time-variable to a corresponding depth-position. This allows highly approximate-yet reproducible-estimations of the thermal conductivity vs. depth. Tests are made on samples incorporating different degrees of sharp structural defects at a certain depth position inside a sample. The proposed methodology opens up new possibilities to perform non-destructive testing; for instance, verifying thermal conductivity homogeneity in a sample, or estimating the thickness of a deviating zone near the sample surface (such as a skin tumor), or testing for presence of other defects. [ABSTRACT FROM AUTHOR]

We derive a generally applicable formula to calculate the precision of multi-parameter measurements that apply least squares algorithms. This formula, which accounts for experimental noise and uncertainty in the controlled model parameters, is then used to analyze the uncertainty of thermal property measurements with pump-probe thermoreflectance techniques. We compare the uncertainty of time domain thermoreflectance and frequency domain thermoreflectance (FDTR) when measuring bulk materials and thin films, considering simultaneous measurements of various combinations of thermal properties, including thermal conductivity, heat capacity, and thermal boundary conductance. We validate the uncertainty analysis using Monte Carlo simulations on data from FDTR measurements of an 80 nm gold film on fused silica. [ABSTRACT FROM AUTHOR]

Porous polyimide fiber enjoys a good reputation as a high temperature resistant thermal insulation material in an aircraft-carrier, a spacecraft, and other military sophisticated products. Understanding its thermal conductivity is especially important for the design optimization and thermal management in these applications. In this study, a modified wire-shape 3ω method is developed to measure the thermal conductivity of individual porous polyimide fibers, utilizing a platinum layer heater/thermometer deposited along the circumferential direction of the fiber. The new method is first validated using a platinum wire with known thermophysical properties such as thermal conductivity at room temperature and then applied to porous polyimide fibers with diverse porosities. The thermal conductivity of porous polyimide fibers at room temperature is 0.06–0.15 W m−1 K−1, which reflects a good thermal insulation performance. [ABSTRACT FROM AUTHOR]

Thermal phenomena in many biological systems offer an alternative detection opportunity for quantifying relevant sample properties. While there is substantial prior work on thermal characterization methods for fluids, the push in the biology and biomedical research communities towards analysis of reduced sample volumes drives a need to extend and scale these techniques to these volumes of interest, which can be below 100 pl. This work applies the 3ω technique to measure the temperature-dependent thermal conductivity and heat capacity of de-ionized water, silicone oil, and salt buffer solution droplets from 24 to 80 °C. Heater geometries range in length from 200 to 700 µm and in width from 2 to 5 µm to accommodate the size restrictions imposed by small volume droplets. We use these devices to measure droplet volumes of 2 µl and demonstrate the potential to extend this technique down to pl droplet volumes based on an analysis of the thermally probed volume. Sensitivity and uncertainty analyses provide guidance for relevant design variables for characterizing properties of interest by investigating the tradeoffs between measurement frequency regime, device geometry, and substrate material. Experimental results show that we can extract thermal conductivity and heat capacity with these sample volumes to within less than 1% of thermal properties reported in the literature. [ABSTRACT FROM AUTHOR]

A thermal property microscopy technique based on frequency domain thermoreflectance (FDTR) is presented. In FDTR, a periodically modulated laser locally heats a sample while a second probe beam monitors the surface reflectivity, which is related to the thermal properties of the sample with an analytical model. Here, we extend FDTR into an imaging technique capable of producing micrometer-scale maps of several thermophysical properties simultaneously. Thermal phase images are recorded at multiple frequencies chosen for maximum sensitivity to thermal properties of interest according to a thermal model of the sample. The phase versus frequency curves are then fit point-by-point to obtain quantitative thermal property images of various combinations of thermal properties in multilayer samples, including the in-plane and cross-plane thermal conductivities, heat capacity, thermal interface conductance, and film thickness. An FDTR microscope based on two continuous-wave lasers is described, and a sensitivity analysis of the technique to different thermal properties is carried out. As a demonstration, we image ∼3 nm of patterned titanium under 100 nm of gold on a silicon substrate, and simultaneously create maps of the thermal interface conductance and substrate thermal conductivity. Results confirm the potential of our technique for imaging and quantifying thermal properties of buried layers, indicating its utility for mapping thermal properties in integrated circuits. [ABSTRACT FROM AUTHOR]

Thermal characterization of materials, especially civil engineering materials, in the way of non-destructive methods, are more and more widespread. In this article, we show an original point of view to describe the used method, the thermal waves, to obtain the thermal impedance of the studied system, using a specific sensor - a fluxmeter. The identification technique, based on a frequential approach, is optimized by applying a random input to the system. This kind of random heating is shown to provide a frequency range where the thermal effusivity is able to be identified and not correlated to another parameter. The strength of the method is also the determination of the contact resistance of the system, that allows to validate the identification process. Experimental results obtained from a sample with well-known thermal properties (polyvinyl chloride) are used to validate the proposed method. [ABSTRACT FROM AUTHOR]

This work presents a method to measure the thermal conductivity and heat capacity of electrically conducting small-volume liquid samples using the 3ω technique. A mathematical model of heat transfer is derived to determine the thermal properties from the 3ω signal considering the device geometry. In order to validate the model, an experimental apparatus has been designed and set up to measure the thermal properties (thermal conductivity and heat capacity) of seven different liquid samples. The results show good agreement with other literature values, demonstrating that the suggested method is effective for measuring the thermal properties of electrically conducting liquids. More importantly, the result with a sample volume of 1 μl demonstrates the resolution of the thermal conductivity as precise as 0.01% which corresponds to a thermal-conductivity change of 10-4 W/m K in the case of water-based solutions. [ABSTRACT FROM AUTHOR]

The 3-omega method is widely used to measure thermal properties of thin films and interfaces. Generally, one-dimensional heat conduction across the film is assumed and the film capacitance is neglected. The change in the in-phase (real part) temperature response for the film-on-substrate case relative to the substrate-only case is, therefore, attributed to the sum of the bulk thermal resistance of the film and the thermal boundary resistance between the film and the substrate. Based on a rigorous and intuitive mathematical derivation, it is shown that this approach represents a limiting case, and that its use can cause significant errors in rather realistic situations when the underlying assumptions are not met. This article quantifies the error by introducing a new parameter called the ratio function R, which modifies the film thermal resistance and mathematically shows that it depends only on three dimensionless parameters that combine thermal properties and geometries of the film and the heated linewidth. A new data reduction scheme is suggested accordingly to determine the film thermal conductivity (cross-plane), anisotropic thermal conductivity ratio between the in-plane direction and the cross-plane direction, and the interface thermal conductance. [ABSTRACT FROM AUTHOR]

A novel calorimeter, termed as the Peltier tip calorimeter, is developed. The calorimeter consists of a single thermocouple junction, called the Peltier tip, which is used as a heater and a sensor simultaneously. We demonstrate that the Peltier tip calorimeter is capable of measuring the heat capacity of a small solid sample with submilligrams of mass and also the thermophysical properties of a liquid such as heat capacity and thermal conductivity. It is also proposed that a Peltier tip be used as a local calorimeter for scanning thermal microscopy. [ABSTRACT FROM AUTHOR]

Although various useful techniques exist for nondestructively measuring homogeneous thermal properties, a few useful type techniques for measuring inhomogeneous thermal properties are reported such that there are many structures, materials, substances, and living things whose thermal properties cannot be measured. The temperature distribution of a target, however, can be nondestructively measured with a very high accuracy using infrared, pyroelectric, ultrasound, or magnetic resonance sensors. In this report, we describe an inverse problem technique for determining in situ the thermal conductivity distribution of a target having an arbitrary geometry using only internal steady temperature distribution measurements. The target distribution is directly determined by linearly solving heat transfer equations as the first-order partial differential equations in which temperature distributions and reference thermal conductivities of the region of interest are used as inhomogeneous coefficients. Under proper configurations of reference regions and thermal sources/sinks, this technique enables the determination of the conductivity distribution without disturbing the temperature distribution. A stable numerical solution that considers measurement noise and improper configurations of reference regions and thermal sources/sinks is also described. Technique feasibility is confirmed using two-dimensional problems through simulations and experiments using conventional infrared thermography. [ABSTRACT FROM AUTHOR]

Thermal diffusivity and specific heat can be estimated from thermal conductivity measurements made using a standard needle probe and a suitably high data acquisition rate. Thermal properties are calculated from the measured temperature change in a sample subjected to heating by a needle probe. Accurate thermal conductivity measurements are obtained from a linear fit to many tens or hundreds of temperature change data points. In contrast, thermal diffusivity calculations require a nonlinear fit to the measured temperature change occurring in the first few tenths of a second of the measurement, resulting in a lower accuracy than that obtained for thermal conductivity. Specific heat is calculated from the ratio of thermal conductivity to diffusivity, and thus can have an uncertainty no better than that of the diffusivity estimate. Our thermal conductivity measurements of ice Ih and of tetrahydrofuran (THF) hydrate, made using a 1.6 mm outer diameter needle probe and a data acquisition rate of 18.2 points/s, agree with published results. Our thermal diffusivity and specific heat results reproduce published results within 25% for ice Ih and 3% for THF hydrate. [ABSTRACT FROM AUTHOR]

3ω methods are commonly used to measure the thermal conductivity of a substrate adjacent to a strip heater or the thermal conductivity and specific heat of a suspended wire. Here we consider the general case of a line heater that is also used to sense temperature. Analysis of all harmonics is presented in terms of generic thermal and electrical transfer functions and is readily adapted to other experimental configurations. We identify voltage signals at 2ω and 1ω that contain the same information about the thermal properties as the 3ω signal. The 2ω voltage requires a dc offset at the current source. The 1ω voltage requires a very stable current source, but eliminates the need for higher-harmonic detection, and is advantageous for studying the dynamics of systems with very fast thermal response times. The 1ω, 2ω, and 3ω methods compare favorably with experiments using a suspended platinum wire and a line heater on a Pyrex substrate. With a modern lock-in amplifier, no common-mode voltage subtraction is necessary, which simplifies the experiment compared to the common practice of balancing a bridge or using a multiplying digital-to-analog converter. We also show that the widespread practice of using a voltage source to approximate a current source is only valid when the sample resistance is small compared to the total electrical resistance of the circuit, and derive and experimentally verify a correction factor to be used otherwise. [ABSTRACT FROM AUTHOR]

Transient hot probe methods are widely used for the measurement of thermal properties in semi-infinite media. In this article, the three-dimensional temperature impulse response of a rectangular probe is analyzed using an analytical solution based on the Green’s functions, such that two characteristic times relative to the asymptotic behaviors of the probe can be calculated. A strategy for the estimation of two uncorrelated properties is deduced from this approach. The identification technique, based on a fractional model approach, is optimized by applying a random input heat flux to the probe. This kind of random heating is shown to provide a frequency content in the range where both the thermal conductivity and thermal effusivity are uncorrelated. Some experimental results obtained with samples with well-known thermal properties are used to validate the proposed method. [ABSTRACT FROM AUTHOR]

Refrigerators for space and other applications working around 100 mK require lightweight components with good thermal properties. We have measured the thermal properties of high-purity (99.95%) magnesium, which is five times lighter than copper, over the 60–150 mK range and found that it is well-behaved down to these temperatures. Both conductivity and heat capacity are in good agreement with extrapolations from measurements at higher temperatures. The heat capacity per unit volume is about the same as copper and the thermal conductivity about 2.7 times lower than copper of similar residual resistivity ratio, as expected from magnesium’s higher room-temperature resistivity. [ABSTRACT FROM AUTHOR]

There are growing needs to measure the thermal properties of small-volume liquid samples in various fields of bioengineering and microfluidics. Accordingly, there have been efforts toward miniaturization of the sensing device without substantially sacrificing the sensitivity. The minimum sample volume required for quantitative thermal analysis is currently in the 10 nl scale. In this work, we describe microfabricated sensors and a modified three-omega data-analysis scheme to determine the thermal conductivity k and volumetric heat capacity ρcp of samples of a few hundred picoliters. In experiments using several reference liquids, the technique measured k and ρcp of 750 and 375 pl samples. The measurement accuracies were ∼10% for k and ∼15% for ρcp. [ABSTRACT FROM AUTHOR]

Conventional techniques for thermal conductivity measurements can lead to unreliable results when applied to nanostructures because heaters and temperature sensors needed for the measurement cannot have a negligible size and therefore perturb the result. In this paper, we focus on the 3ω technique, applied to the evaluation of the thermal conductivity of suspended silicon nanoribbons. We introduce a numerical approach based on the finite element solution of the electrical and thermal transport equations and compare its results with those of conventional methods. We show that with our approach we achieve an excellent fit of the experimental data, in particular, for nanostructured materials. [ABSTRACT FROM AUTHOR]

This paper presents a new method dedicated to thermal properties (conductivity and diffusivity) measurement of dry bulk materials including powders. The cylindrical three layers experimental device (brass/bulk material/stainless steel) and the principle of the measurement method based on a crenel thermal excitation are presented. The one-dimensional modeling of the system is used for a sensitivity analysis and to calculate the standard deviation of the estimation error. Experimental measurements are carried out on three bulk materials: glass beads, cork granules, and expanded polystyrene beads. The estimated thermal properties are compared with the values obtained by other measurement methods. Results are in good agreement with theoretical predictions: both thermal conductivity and diffusivity can be estimated with a good accuracy for low density material like cork granules or expanded polystyrene beads since only thermal diffusivity can be estimated for heavier materials like glass beads. It is finally shown that this method like all transient methods is not suited to the thermal characterization of wet bulk materials. [ABSTRACT FROM AUTHOR]

In this paper, we describe the thermal conductivity measurement of single-walled carbon nanotubes thin film using a laser point source-based steady state heat conduction method. A high precision micropipette thermal sensor fabricated with a sensing tip size varying from 2 μm to 5 μm and capable of measuring thermal fluctuation with resolution of ±0.01 K was used to measure the temperature gradient across the suspended carbon nanotubes (CNT) film with a thickness of 100 nm. We used a steady heat conduction model to correlate the temperature gradient to the thermal conductivity of the film. We measured the average thermal conductivity of CNT film as 74.3 ± 7.9 W m-1 K-1 at room temperature. [ABSTRACT FROM AUTHOR]